Meaning of subatmospheric

sub•at•mos•pher•ic

Pronunciation: (sub"at-mus-fer'ik, -fēr'-), [key]
— adj.
  1. (of a quantity) having a value lower than that of the atmosphere: subatmospheric temperatures.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.